Bump python-novaclient version

The recently added support for nova API microversions 2.91 and 2.92
necessitate a newer version of python-novaclient. Make it so.

Change-Id: I40a77334e4aee2e196062c38a0bb70f8f3079b44
Signed-off-by: Stephen Finucane <sfinucan@redhat.com>

Author: stephenfin

requirements.txt

@@ -14,6 +14,6 @@ osc-lib>=2.3.0 # Apache-2.0
 oslo.i18n>=3.15.3 # Apache-2.0
 oslo.utils>=3.33.0 # Apache-2.0
 python-keystoneclient>=3.22.0 # Apache-2.0
-python-novaclient>=17.0.0 # Apache-2.0
+python-novaclient>=18.1.0 # Apache-2.0
 python-cinderclient>=3.3.0 # Apache-2.0
 stevedore>=2.0.1 # Apache-2.0